A.T. Robertson Commentary Revelation 10:4

"And when the seven thunders uttered [their voices], I was about to write: and I heard a voice from heaven saying, Seal up the things which the seven thunders uttered, and write them not." — Revelation 10:4 (ASV)

I was about to write (ημελλον γραφειν). Imperfect active of μελλω (double augment as in Joh 4:47; 12:33; 18:32) and the present (inchoative) active infinitive of γραφω, "I was on the point of beginning to write," as commanded in 1:11,19.

Seal up (σφραγισον). Aorist active imperative of σφραγιζω, tense of urgency, "seal up at once."

And write them not (κα μη αυτα γραψηις). Prohibition with μη and the ingressive aorist active subjunctive of γραφω, "Do not begin to write." It is idle to conjecture what was in the utterances. Compare Paul's silence in 2 Corinthians 12:4.